The present invention concerns improvements in dynamometers for testing internal combustion engines. More specifically, the inventions disclosed and claimed herein arose out of a program involving design and development of a dynamometer particularly suited for running rapid automated tests of Buick V-6 engines as they come off the engine assembly line. Such a testing environment puts a premium on simple, rapid and reliable means for connecting the engine to be tested to the dynamometer unit. Both the time available for making the connections and the skill of the operator in the assembly plant environment are generally less than those which exists in a laboratory test environment. Therefore, there is a greater possibility that errors may be made in the connections which may produce conditions detrimental to the accuracy or integrity of the equipment.
As stated above, the engine for which the test system was developed is a 90 degree V-6 engine having a rated torque of approximately 300 foot pounds. The engine is suspended on a J-hook from an overhead beam during the test, and the dynamometer itself is also separately suspended. The engine and dynamometer are clamped together for testing by means of air-driven screws. The dynamometer itself is a water brake type unit manufactured by Go-Power Corporation of Palo Alto, Calif. For purposes of the present program, applicant had to develop an improved input end of the dynamometer as well as an adapter for interfacing the input of the dynamometer to the output of the tested engine.
The driving connection between the adapter and the engine is effected by means of three axially extending locating pins positioned to engage three holes located at 120 degree intervals in the engine flywheel (for use with manual transmissions) or engine-mounted flexible drive plate (for use with automatic transmissions). Thus, all that is necessary to establish a mechanical driving connection between the engine and the dynamometer is to bring the axes of these two units into substantial alignment, bring the pins of the dynamometer adapter into angular alignment with the holes in the flywheel or flexible drive plate and then bolt the two units together with two air-driven bolts.
Early experience with this unit produced several structural failures in the dynamometers. The source of the excessive or unusual loading on the dynamometer was not readily apparent, but it was ultimately traced to two phenomena.
It was discovered that one of the problems resulted from an excessive axial thrust applied from the engine toward the dynamometer, a type of loading which normally, if it exists at all in an engine, is absorbed within the engine rather than being transmitted from the engine to the dynamometer. The particular source of this load was traced to improper interfacing of the three locating pins on the dynamometer with the three holes in the flexible drive plate. The problem did not exist on engines equipped with flywheels for use with manual transmissions. In the relatively hurried and uncontrolled conditions of assembly line testing, the operators were not always establishing proper angular alignment of the pins with the pin-receiving holes in the flexible drive plate. With the pins and holes out of registry, tightening of the two clamping bolts resulted in the pins resiliently flexing the drive plate toward the engine. Thus, the axial deflection of the drive plate produced a large axially directed load on the pins, which load was transmitted through the entire adapter structure into the input shaft of the dynamometer, ultimately producing failure of the dynamometer.
A second source of dynamometer failures was traced to the nature of the engine configuration. A change in the firing program of the V-6 engine from one calling for firing of cylinders at three of the four 90 degree intervals of each revolution of the crankshaft to a program wherein a cylinder fired at every 120 degree interval of rotation produced three torque reversals per revolution of the crankshaft. It was discovered that torque peaks or spikes varying from +2000 foot-pounds to -1500 foot-pounds were occurring with this engine. Without a flywheel or torque converter to mask or partially absorb these severe torque reversals, the tested engines having flexible drive plates were producing torsional type of failures in the dynamometers.
Accordingly, the discovery of these two unexpected sources of extraordinary dynamometer loading led to the solution of the problems by the incorporation of two novel features in the dynamometer.
The problem produced by improper registry of the locating pins with the holes in the flexible drive plate was eliminated by the use of a thrust bearing mounted on the dynamometer input shaft in such a way that any axial loads directed toward the dynamometer were directed through such thrust bearing into the dynamometer housing, rather than onto the dynamometer input shaft.
The excessive torque reversal loading problem was overcome by the use of the torque absorber such as is normally used as part of the friction disc of a manual transmission clutch.